The phylogeny of Ryocalanoidea (Copepoda, Calanoida) based on morphology and a multi-gene analysis with a description of new ryocalanoidean species

Abstract

Abstract Two new species of ryocalanoid copepods (Crustacea: Calanoida), Ryocalanus squamatus sp. nov. and Yrocalanus kurilensis sp. nov. are described together with a female of Ryocalanus infelix Tanaka, 1956, type species for the genus Ryocalanus Tanaka, 1956, from abyssal depths in the Kurile-Kamchatka trench. The new species can be assigned to the superfamily Ryocalanoidea based on the segmentation and armature of the swimming legs and the modification of the male right antennule. A new interpretation of the fusions of segments in the male right antennule of Ryocalanus shows the marked differences between the ryocalanoidean genera. The status of Ryocalanoidea within the Calanoida is discussed based on morphology and a first molecular multi-gene analysis with cytochrome oxidase subunit I, cytochrome b, nuclear ribosomal 18S and 28S rDNA and internal transcribed spacer 2. This analysis supports the close interrelationship between Ryocalanoidea and Spinocalanoidea. The monophyletic status of Ryocalanoidea could not be retrieved in the phylogenetic analysis, as specimens of Yrocalanus formed a clade within Spinocalanoidea. The inconclusive results between morphological and molecular analyses are discussed with a proposition to keep the current system until more males of taxa belonging to the Spinocalanoidea are discovered, as the male antennule plays a crucial role in the interpretation of relationships between Ryocalanoidea and Spinocalanoidea.